Evaluation of qPCR reference genes for taimen (Hucho taimen) under heat stress

As a powerful and attractive method for detecting gene expression, qRT-PCR has been broadly used in aquaculture research. Understanding the biology of taimen (Hucho taimen) has drawn increasing interest because of its ecological and economic value. Stable reference genes are required for the reliable quantification of gene expression, but such genes have not yet been optimized for taimen. In this study, the stability levels of 10 commonly used candidate reference genes were evaluated using geNorm, NormFinder, BestKeeper, and RefFinder. The expression levels of the 10 genes were detected using 240 samples from 48 experimental groups consisting of 40 individuals treated under four heat-stress conditions (18, 20, 22, and 24 °C) for 24 h and 26 °C for 4, 24, 48, and 72 h. Six tissues (blood, heart, brain, gill, skin, and liver) were collected from each individual. Ribosomal protein S29 (RPS29) and ribosomal protein L19 (RPL19) were the most stable genes among all of the samples, whereas 28S ribosomal RNA (28S rRNA), attachment region binding protein (ARBP), and 18S ribosomal RNA (18S rRNA) were the least stable. These results were verified by an expression analysis of taimen heat-stress genes (heat shock protein 60, hsp60, and heat shock protein 70, hsp70). In conclusion, RPS29 and RPL19 are the optimal reference genes for qRT-PCR analyses of taimen, irrespective of the tissue and experimental conditions. These results allow the reliable study of gene expression in taimen.

Effects of Dietary Glutathione on the Growth Performance, Skin Mucus Antioxidant Capacity, and Immune Responses of Juvenile Taimen Hucho Taimen

The effects of dietary glutathione on growth performance, skin antioxidant capacity, and immune responses and of juvenile taimen (Hucho taimen) were investigated. The experimental fish had a mean initial weight of 5.36 ± 0.13 g and were fed for eight weeks on diets containing graduated amounts of glutathione (0, 100, 200, 400, and 800 mg kg−1). After the 7 d lipopolysaccharide challenge, the immune parameters of the skin mucus, and antioxidant ability were determined. The treatment groups (400 – 800 mg kg−1) showed a higher survival rate and weight gain rate (P < 0.05). There were higher levels of skin mucus protein, lysozyme activity, and alkaline phosphate activity associated with dietary glutathione supplementation (P < 0.05). Dietary glutathione supplementation improved the minimal inhibitory concentration and antimicrobial activity of the skin mucus (P < 0.05). Fish in the treatment groups showed higher superoxide dismutase, glutathione peroxidase, and catalase activity (P < 0.05), whereas the malondialdehyde content was lower (P < 0.05) than those in the control group. Supplementary glutathione decreased the expression levels of TNF-α, IL1β, IL6, IL8 in the skin and ensured the relatively high expression levels of IκBα after lipopolysaccharide challenge. In conclusion, dietary glutathione (400 – 800 mg kg−1) improved the growth performance, decreased lipopolysaccharide-induced skin inflammatory response, indicating that glutathione has the potential anti-inflammatory effects for preventing inflammation diseases in juvenile taimen.

Evaluation of qPCR Reference Genes For Taimen (Hucho Taimen)

As a powerful and attractive method for detecting gene expression, qRT-PCR has been broadly used in aquacultural research. Understanding the biology of taimen (Hucho taimen) has attracted increased interest because of its ecological and economic values. Stable reference genes are required for the reliable quantification of gene expression, but such genes have not yet been optimised for taimen. In this study, the stability levels of 10 commonly used candidate reference genes were evaluated using four methods, geNorm, NormFinder, BestKeeper and RefFinder. The expression levels of the 10 genes were detected using samples from 48 experimental groups that consisted of six tissues (blood, heart, brain, gill, skin and liver) collected under five heat-stress conditions (18, 20, 22, 24 and 26°C) and four heat-stress processing times (4, 24, 48 and 96 h). RPS29 and RPL19 were the most stable genes among all the samples, whereas 28S rRNA, ARBPR and 18S rRNA were the least stable. These results were verified by an expression analysis of the heat-stress genes (hsp60 and hsp70) of taimen. In conclusion, RPS29 and RPL19 are the optimal reference genes for qRT-PCR analyses of taimen, irrespective of the tissue and experimental conditions, and these results allow the reliable study of gene expression in taimen.

Maximum weight of Siberian taimen Hucho taimen (Pallas) in its range

In most western regions, Siberian taimen has become a rarity in its range. At present, only a few refugiums of the Siberian and Far Eastern rivers still have groups of Siberian taimen, where fish of the maximum size are recorded. In the east of its range, the rivers that flow into the southern part of the Sea of Okhotsk: The Amur, Uda and Tugur, are the few areas where the Siberian taimen groups are still preserved in good condition in uninhabited places. On the example of p. Tugur (Tuguro-Chumikansky district of the Khabarovsk Territory, Sea of Okhotsk), where there are no roads and a small population, the authors studied the local grouping of Siberian taimen, where individuals of maximum size are still not uncommon. The remaining areas of the range are considered according to scientific publications. Fish of the maximum size are very rare, which is logical: the number of extreme values of the size-age range is minimal. In 2007-2018, in the Tugur River, individuals aged 6-10 years were the maximum (27.6%), and 31-35 years – the minimum (0.9%) of the age range. The archives of the sport fishing base in the Tugur River basin for 2008-2020 showed that the maximum body length of the Siberian taimen was 165 cm, and the maximum body weight was 51.12 kg. Neither in the era of black-and-white photography, nor in the era of video, there is no documentary evidence of the Siberian taimen with a body length of more than 170 cm.

First results of acoustic tags using for studies of migrations of siberian taimen Huho taimen (Salmonidae) in the Tugur River basin (northwestern Okhotsk Sea)

Method of acoustic tagging of large-sized fish in a medium river is successfully tested for the case of siberian taimen Hucho taimen in the Tugur River. Algorithm of fish anesthesia and acoustic tag input into its body cavity is developed. For successful tagging, total duration of the process, including anesthesia, should not exceed 5 minutes. The best results of tagging are obtained for fish with a body length of 110–130 cm, which tolerate anesthesia easily. In 2017–2019, 25 out of 29 tagged fish were registered by acoustic equipment that indicates high efficiency of the method (86.2 %). Distance from the release point to the point of tag registration varied from 0.2 to 39.8 km. Some fish crossed almost completely the buoy-controlled section of the river that indicates a rather high migration potential of siberian taimen. On the background of high individual diversity of migration activity, two principally different behavioral strategies are distinguished — «residents» staying in one place up to 2 months and «nomads» migrating to a distance up to 30 km per day. The radius of taimen migration increases usually in May and September and decreases in August. The seasonal increasing is associated with feeding migrations: taimen feed on downstream juveniles of chum salmon Oncorhynchus keta and prespawning minnows Rhynchocypris lagowskii in May and on chum adults migrating to spawning grounds in September. During twilight and at night, the migrations are usually more active, but they are less visible and shorter in the morning and afternoon. Correspondingly, the main feeding of taimen is assumed in the twilight and dark time, whereas a supporting feeding in the daytime.